Micro-spring packages generally involve an integrated circuit arranged on a substrate where the integrated circuit has contact pads, referred to here as the pad chip. Another circuit package having protruding contact springs, referred to here as the spring chip, is aligned with the pad chip such that the springs contact the pads. An adhesive holds the springs in contact with the pads.
The process typically includes dispensing an uncured adhesive onto the pads prior to being brought into contact with the springs. Once the springs contact the pads, the adhesive is cured, converting it into a robust, solid mold. Curing may include exposing the adhesive to UV light. An example of such a process is given in U.S. Pat. No. 6,213,789, “Method and Apparatus for Interconnecting Devices Using an Adhesive,” issued Apr. 10, 2001.
However, this approach does not scale well for packages having thousands of spring interconnects contacting large sized pads. The contacts fail when subjected to even mild thermal soaks. One issue that arises from the size of the pads. Generally, UV curing involves exposing the adhesive to UV light from underneath the pad. The larger pads block the light, resulting in partially cured adhesive. When the partially cured adhesive heats up in a thermal soak, it can migrate into the contact area, causing the contacts to fail. This thermally-induced effect means using thermally set adhesives instead of UV-cured adhesives would also result in similar contact failures.